require "securerandom"
require "active_support/core_ext/string/access"

# Rails 3 support for ActionDispatch::RequestId introduced in Rails 4
# https://github.com/rails/rails/blob/master/actionpack/lib/action_dispatch/middleware/request_id.rb
module Trifle
	module Ruby
		module Middleware
			# Makes a unique request id available to the action_dispatch.request_id env variable (which is then accessible through
			# ActionDispatch::Request#uuid) and sends the same id to the client via the X-Request-Id header.
			#
			# The unique request id is either based off the X-Request-Id header in the request, which would typically be generated
			# by a firewall, load balancer, or the web server, or, if this header is not available, a random uuid. If the
			# header is accepted from the outside world, we sanitize it to a max of 255 chars and alphanumeric and dashes only.
			#
			# The unique request id can be used to trace a request end-to-end and would typically end up being part of log files
			# from multiple pieces of the stack.
			class RequestId
				def initialize(app)
					@app = app
				end

				def call(env)
					env["action_dispatch.request_id"] = external_request_id(env) || internal_request_id
					@app.call(env).tap { |_status, headers, _body| headers["X-Request-Id"] = env["action_dispatch.request_id"] }
				end

				private
				def external_request_id(env)
					if request_id = env["HTTP_X_REQUEST_ID"].presence
						request_id.gsub(/[^\w\-]/, "").first(255)
					end
				end

				def internal_request_id
					SecureRandom.uuid
				end
			end
		end
	end
end
